Electrically small, wideband, high dynamic range antenna having a serial array of optical modulators

Abstract

A magnetic field sensor which can be used as an active antenna is disclosed that is capable of small size, ultrawideband operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators, that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.

I claim: 
     
       1. A wideband, high linear dynamic range sensor for detecting incident electromagnetic radiation over a bandwidth from about DC to at least 10 GHz, comprising: (a) a serial array of a plurality of transducing means coupling each transducing means with the incident electromagnetic radiation for providing an output signal indicative of the magnitude of the incident electromagnetic radiation;   (b) bias means, coupled to the array, for providing bias energy to every transducing means of the array;   (c) energy focusing means for collecting the incident electromagnetic radiation in a collected signal and for distributing the collected signal to the array so that the transducing means provide the output signal indicative of the magnitude of the incident electromagnetic radiation; and   (d) negative, analog feedback means for coupling negative, analog feedback from the output signal to the energy focusing means to improve the linear dynamic range of the sensor wherein the transducing means are optical modulators for sequentially modulating the bias means in the form of an optical carrier signal transmitted through the optical modulators in series to modulate the optical carrier signal in response to the incident electromagnetic radiation.     
     
     
       2. The wideband, high linear dynamic range sensor, comprising (a) an array of serially connected Mach-Zehnder interferometers forming an optical circuit having an optical output;   (b) at least one electric dipole antenna for receiving an incident electric field and for electrically coupling the radiation received from the incident electric field to the interferometers;   (c) a laser source for feeding an optical carrier signal to the array of interferometers;   (d) a photodetector for converting the optical output of the array to an RF signal; and   (e) feedback means responsive to the RF signal for providing feedback from the RF signal to the electric dipole antenna to increase linear dynamic range for the sensor.   
     
     
       3. A wideband, high linear dynamic range sensor for detecting incident electromagnetic radiation over a bandwidth from about DC to at least 10 GHz, comprising: (a) a serial array of Mach-Zehnder interferometers coupling with the incident electromagnetic radiation to generate an array output indicative of the magnitude of the incident electromagnetic radiation;   (b) a laser source, coupled to the array to bias the interferometers by providing an optical carrier signal sequentially to every interferometer, the array output being a modulated optical signal arising from sequentially modulating the optical carrier signal in the interferometers in the serial array;   (c) at least one electric dipole antenna for collecting the incident electromagnetic radiation in a collected signal indicative of the magnitude of the incident radiation and for distributing the collected signal to interferometers; and   (d) negative, analog feedback means for coupling negative, analog feedback from the array output to modulate the optical carrier signal to improve the linear dynamic range of the sensor, the feedback means including a photodetector for converting the array output into an RF signal.   
     
     
       4. A wideband, high linear dynamic range sensor for detecting incident electric fields in the range form DC to at least 10 GHz comprising: (a) an array of at least three serially connected Mach-Zehnder interferometers, the array producing a single output with enhanced amplitude modulation because of the series of interferometers;   (b) an electric dipole antenna associated with each interferometer for receiving the incident electric field and for coupling the radiation received from the incident electric field to each interferometer;   (c) a laser source for feeding an optical carrier signal to the interferometers, the interferometers modulating the carrier signal in response to the incident electric field to produce the output;   (d) a photodetetor optically connected in series with the output for converting the output to an RF signal representative of the incident electric field; and   (e) optionally, feedback means responsive to the RF signal for providing feedback to each electric dipole antenna to provide substantially larger linear dynamic range for the bandwidth.   
     
     
       5. The sensor of claim 4 further comprising low noise amplifier connected to the photodetector for amplifying the RF signal.